USB serial buses have become pervasive in even basic embedded system designs with designers using off-the-shelf USB 2.0 modules to bring this capability to their design. Validating and troubleshooting these buses once integrated can be cumbersome without the right test tools. This article provides background information on USB and how it works followed by a hands on example of using an oscilloscope for validating and troubleshooting a USB 2.0 bus.